The present invention relates to a field-sequential type display device and display method for performing a display by synchronizing the switching of colors of light incident on a display element with the light control in the display element based on display data of respective colors, and also relates to a color-filter type display device and display method for performing a color display by synchronizing the incidence of white light on a display element having color filters with the light control in the display element based on display data of respective colors.
Along with the recent development of so-called information-oriented society, electronic apparatuses, such as personal computers and PDA (Personal Digital Assistants), have been widely used. With the spread of such electronic apparatuses, portable apparatuses that can be used in offices as well as outdoors have been used, and there are demands for small-size and light-weight of these apparatuses. Liquid crystal display devices are widely used as one of the means to satisfy such demands. Liquid crystal display devices not only achieve small size and light weight, but also include an indispensable technique in an attempt to achieve low power consumption in portable electronic apparatuses that are driven by batteries.
The liquid crystal display devices are mainly classified into the reflection type and the transmission type. In the reflection type liquid crystal display devices, light rays incident from the front face of a liquid crystal panel are reflected by the rear face of the liquid crystal panel, and an image is visualized by the reflected light; whereas in the transmission type liquid crystal display devices, the image is visualized by the transmitted light from a light source (back-light) placed on the rear face of the liquid crystal panel. Since the reflection type liquid crystal display devices have poor visibility because the reflected light amount varies depending on environmental conditions, transmission type color liquid crystal display devices using color filters are generally used as the display devices of personal computers displaying full-color images.
As the color liquid crystal display devices, TN (Twisted Nematic) type liquid crystal display devices using switching elements such as a TFT (Thin Film Transistor) are widely used at present. Although the TFT-driven TN type liquid crystal display devices have better display quality compared to an STN (Super Twisted Nematic) type, they require a back-light with high intensity to achieve high screen brightness because the light transmittance of the liquid crystal panel is only 4% or so at present. For this reason, a lot of power is consumed by the back-light. Besides, since a color display is achieved using color filters, a single pixel needs to be composed of three sub-pixels, and there are problems that it is difficult to provide a high-resolution display, and the purity of the displayed colors is not sufficient.
In order to solve such problems, the present inventor et al. developed field-sequential type liquid crystal display devices (see, for example, T. Yoshihara et al., AM-LCD '99 Digest of Technical Papers, p. 185, 1999; and T. Yoshihara et al., SID '00 Digest of Technical Papers, p. 1176, 2000). Since such a field-sequential type liquid crystal display device does not require sub-pixels, it is possible to easily achieve a higher resolution display compared to a color-filter type liquid crystal display device. Moreover, since the field-sequential type liquid crystal display device can use the color of light emitted by the light source as it is for display without using a color filter, the displayed color has excellent purity. Furthermore, since the light utilization efficiency is high, this device has the advantage of low power consumption. However, in order to realize a field-sequential type liquid crystal display device, a high-speed responsiveness (2 ms or less) of liquid crystal is essential.
In order to provide a field-sequential type liquid crystal display device with significant advantages as mentioned above or increase the speed of response of a color-filter type liquid crystal display device, the present inventor et al. are conducting research and development on the driving of liquid crystal such as a ferroelectric liquid crystal having spontaneous polarization, which may achieve 100 to 1000 times faster response compared to a conventional type, with a switching element such as a TFT. In the ferroelectric liquid crystal, as shown in FIG. 1, the long-axis direction of the liquid crystal molecule is tilted by the application of voltage. A liquid crystal panel sandwiching the ferroelectric liquid crystal therein is sandwiched by two polarization plates whose polarization axes are orthogonal to each other, and the intensity of transmitted light is changed using the birefringence caused by a change in the long-axis direction of the liquid crystal molecule.
FIG. 2 illustrate an example of time chart of display control in a conventional field-sequential type liquid crystal display device, wherein FIG. 2(a) shows the scanning timing of each line of the liquid crystal panel, and FIG. 2(b) shows the ON timing of red, green and blue colors of the back-light. One frame is divided into three sub-frames, and, for example, as shown in FIG. 2(b), red light is emitted in the first sub-frame, green light is emitted in the second sub-frame, and blue light is emitted in the third sub-frame.
Meanwhile, as shown in FIG. 2(a), for the liquid crystal panel, image data writing scanning and erasing scanning are performed within a sub-frame of each of red, green and blue colors. However, the timings are adjusted so that the start timing of the writing scanning coincides with the start timing of each sub-frame, and the end timing of the erasing scanning coincides with the end timing of each sub-frame, and the time necessary for each of the writing scanning and the erasing scanning is set to a half of each sub-frame. During the writing scanning and the erasing scanning, voltages which are equal in magnitude and different in polarity based on the same image data are applied to the liquid crystal panel. Moreover, the light emission time of each color is equal to the time of a sub-frame (see, for example, Japanese Patent Application Laid-Open No. 11-119189/1999).
Field-sequential type liquid crystal display devices have the advantages of high light utilization efficiency and reducing power consumption. However, in order to mount a field-sequential type liquid crystal display device on a portable apparatus, a further reduction in power consumption is required. Such a requirement for reduction in power consumption is directed not only to a field-sequential type liquid crystal display device using a liquid crystal element as a display element, but also to field-sequential type display devices using other display elements such as a digital micro mirror device (DMD) and also to color-filter type display devices similarly.